Team:SBS SH 112144/Lysozyme


A brief history about lysozyme

Lysozyme exists as an antibacterial mechanism across multiple kingdoms of life. The first human experience with antibacterial lysozyme was in 1909, when Laschtschenko discovered the lysozyme within egg white and its capability of forming a barrier between the outside world and the embryo inside. But the enzyme was not properly given a name until 1922, when the nobel laureate, Alexander Fleming identified its basic function of “ rapidly lysing (ie.., dissolving) certain bacteria”. In 1965, structural biologist David Chilton Phillips was able to conduct an X-ray crystallography on lysozyme and explain the protein’s role of chemical catalysis with its physical structure. Phillips’ theory of chemical lysis with lysozyme was later revised by biochemist Daniel Koshland.

A 3D diagram of lysozyme

Our experience with lysozyme

We use the combination of Novagen Bugbuster and cyanophage lysozyme for the chemical lysis of cyanobacteria. Unlike other gram-negative bacteria such as E. coli, cyanobacteria have a much thicker peptidoglycan layer between the outer membrane and cytoplasmic membrane. In our chemical mixture, bugbuster, which is a commercially classified chemical that is essentially combination of detergents, could break the external layer of polysaccharide and outer membrane. This would expose the peptidoglycan layer.

Our cp-OS lysozyme 1 is a form of bacteriophage lysozyme that exists in virus. Once the cyanophage finish replicating in cyanobacteria, they produce the cyanophage lysozyme to lyse the cyanobacterial cell wall to get out. Through protein blasting of the cyanophage lysozyme, we found its structural similarity and homogeneity with multiple other peptidoglycan binding proteins and even a type of peptidoglycan domain protein from cyanobacterium Nostoc, and this implies the working mechanism of this lysozyme is similar to other lysozyme and is somewhat specific to cyanobacterial peptidoglycan.

Reaction mechanism of lysozyme

1. The aspartic and glutamic acid residues at the active site of the lysozyme would wrap around the glycosidic bond between 6 carbon conponent N-acetylmuramic acid (NAM)and N-acetylglucosamine (NAG) of the carbohydrate section of the peptidoglycan. The carboxyl group on the aspartic acid attacks the carbon on NAM, attaching the aspartic acid to the NAM. Meanwhile, an oxygen on the NAG would pick up the hydrogen proton on the glutamic acid, deprotonating the glutamic acid into a glutamate.

2. The lysis of lysozyme has to take place in aqueous environment. The addition of a water molecule would complete the hydrolysis reaction by protonating the glutamate back to glutamic acid; it would also deprotonate the aspartic acid from the NAM, restoring it back to its reduced form, while leaving a hydroxyl group on the end of NAM. This way, the lysozyme would keep its own structure unchanged while degrading the carbohydrate section of the peptidoglycan into the NAM/NAG components.